The present invention relates to a rotary device that generates a holding torque when energized with a DC current. The device can be used to lower the electrical power consumption in an electro-mechanical brake system.
Electric motor-driven wheel brakes for vehicles are known. When the brake system of a vehicle is designed with electric motor-driven brakes, special attention must be paid to the reliability with which a brake system of this type will operate. In particular, in order to maintain a clamping force and friction torque for a longer period of time (for example, during a decent on a slope or stopping on a hill), the electric motor actuating an electric brake needs to remain constantly energized to prevent a back driving effect through the actuator and therefore loss of the desired clamping force and braking torque. Prolonged energization of the motor may cause overheating of the motor and the associated motor controller due to continuous flow of electrical current.
A number of methods have been proposed to effect reliable braking in an electrically actuated brake system. The object of one example electric braking system is to minimize the load on the batteries for electric motor driven wheel brakes while still maintaining the braking action. This is achieved by supplying actuators of the wheel brakes of each vehicle axle or each vehicle diagonal with current from a separate voltage source, and by actuating the wheel brakes of the front axle before the brakes of the rear axle in at least one braking situation. However, this method may still require prolonged energization of the motor.
Another prior art brake actuator includes as part of the actuator a locking brake mechanism. The locking brake is so configured that the locking brake is without current in the xe2x80x9creleased statexe2x80x9d as well as an xe2x80x9cunreleased statexe2x80x9d and, in this way, a second motor, which is assigned to the locking brake, consumes a negligible current. However, if the electric locking brake is unintentionally activated because of a technical error, or by the driver of the vehicle, this leads to a locking of the motor shaft of the electric motor of the brake actuator and the brake actuator can only then be actuated again when the electric locking brake is specifically released. An automatic release of the locking brake is not possible. In this way, malfunction of the brake actuator occurs when there is an unintended and unplanned activation of the locking brake.
It would be desirable to have a system that overcomes the above disadvantages.
One aspect of the present invention provides a rotary holding device including a rotor assembly including a plurality of teeth and a stator assembly including a plurality of teeth. The stator assembly teeth are positioned adjacent the rotor assembly teeth and a coil is positioned to allow a magnetic flux to align the rotor assembly teeth and the stator assembly teeth when the coil is energized to hold a motor shaft coupled to the device.
In other aspects of the present invention the rotor assembly and the stator assembly can include a steel material that has low magnetic remanence. The teeth of the rotor assembly and the teeth of the stator assembly can be separated by a gap of about 0.15 millimeters. The stator assembly can include a number of teeth equal to a number of teeth of the rotor assembly. The rotor assembly teeth can be of a size equal to the stator assembly teeth. An upper portion of the teeth of the rotor assembly can be gently convex. An upper portion of the teeth of the stator assembly may be gently concave. The teeth of the stator and the teeth of the rotor can be complementary. A pair of ball bearings can support the rotor assembly. End caps can support the ball bearings.
An aspect of the present invention includes a method of operating a rotary holding device in a motor driven brake caliper including energizing a coil of the rotary holding device, aligning rotary teeth and stator teeth of the rotary holding device, holding a motor shaft of the motor which is coupled to the rotary holding device and maintaining a clamping force on a brake rotor while the coil is energized.
Other aspects of the method of the present invention include de-energizing the coil to release the clamping force. The rotary teeth and stator teeth can be aligned by a magnetic flux. The coil can be energized with current at a level less than the current required for the motor to maintain a clamping force on the brake rotor. The clamping force can be maintained at a low noise level.
A further aspect of the present invention provides a brake rotor clamping system including means for generating magnetic flux, means for aligning rotor teeth and stator teeth, means for holding a motor shaft, and means for maintaining a clamping force on the brake rotor while the magnetic flux is generated.
Other aspects of the present invention further include means for stopping the magnetic flux to release the clamping force.